President-elect is the term used to describe the successful candidate in a US presidential election, between his election and his inauguration, when he formally takes office. In the modern era, many outgoing Presidents have worked with the President-Elect to ensure a smooth transition. However, the President-Elect has no official duties; he is only mentioned in the Twentieth Amendment to the Constitution in the context of what happens if he dies before taking office:
If, at the time fixed for the beginning of the term of the
President, the President elect shall have died, the Vice President electshall become President...